I shoot Knight DISC Extremes, and have three of them so I can take the family. They have a great barrel for pure lead conicals, so I am not sure if what I am going to say will fully apply to other muzzleloaders.
My load is 85 grains by volume of Blackhorn 209, two 0.06" thick vegetable fiber wads (reduces flame scorching the bullet), a 460 grain lead conical from No Excuses (50 caliber), and a Fiocchi 209 primer.
I measure my first load by VOLUME, weigh it on a powder scale, then weigh all my following loads. You do it that way because various powders weigh much differently than the measure volumetrically. An 85 grain volume measurement for BH209 is 59.5 grains by weight. To calculate the weight (Blackhorn 209 only!!) take the volumetric measurement and multiply it by 0.7:
85 grains by volume x 0.7 = 59.5 grains by weight
After weighing my loads, I put them in waterproof vials. I really like these off of eBay.
Some of my current thinking behind my muzzleloader load.
1) Most new muzzleloaders have fast twist barrels for stabilizing a bullet in a sabot. If a barrel was specifically designed for a conical, they would be slower twist. These fast twist barrels best stabilize long heavy bullets like the 460 grain I shoot, better than shorter lighter bullets. It is the same concept in today's long-range hunting rifles, twist rates are getting faster to shoot long heavy bullets.
2) 50 caliber has a huge frontal surface area and will shed energy quickly. I didn't realize it until a few years ago, but a roundball loses a ton of energy even at fairly modest ranges (50-75 yards). Again a long heavy bullet helps overcome that and retains energy better downrange. This is the concept behind Ballistic Coefficient (BC). This is the very concept with today's long-range rifle hunting bullets (along with an aerodynamic shape).
3) Lead has far more density than copper, so for a given load, you will have better retained energy downrange with an all lead bullet. (Again, same concept in rifle hunting bullets, all copper bullets don't retain energy as well as jacketed lead bullets.)
3) Years ago I had accuracy issues with lead conicals, a guy told me to shoot a more modest powder load. I have since seen accuracy deteriorate when I get to 90 grains (by volume) and beyond in my muzzleloaders. I believe what is happening is the lead is stripping from the rifling.
4) I feel Blackhorn 209 is by far the best powder for accuracy out there, simply due to the minimal residue left, and that you can shoot a fouling shot and with the powder being minimally corrosive, you can then hunt on a fouled barrel.
5) Blackhorn 209 seems to be sensitive to primers that push the bullet off the compressed load before the powder ignites. That issue has probably been the major accuracy issue for me when shooting BH209. Fiocchi primers have the energy to reliably ignite the powder, but are also a softer primer, not affecting the compression of the load.
6) I think No Excuses bullets (from Utah) are fantastic bullets and the best lead conicals in production. The guy who makes them die sizes them, which precision sizes them for the bore. They are also prelubed.
7) Not all barrels shoot lead conicals well. I have been told that barrels with deeper "lands and grooves" are better conical barrels. I do know my Knights shoot lead conicals lights out.
8) 460 grains may seem like a crazy heavy bullet, but for states that require open sights, where you are limited to 150 yards or so, the trajectory is reasonable, and the energy retention is excellent in those ranges.